The transmission of optical signals in an optical communication system may be limited by optical effects such as chromatic dispersion., Optical signals may be transmitted as pulses of light in an optical fiber. When light propagating within an optical fiber undergoes chromatic dispersion, the light is delayed within the optical fiber. The delay causes spreading of the light pulses, which may affect the performance of the system. The specific amount of dispersion that an optical signal undergoes varies depending upon the wavelength of the optical signal. The extent to which dispersion varies as a function of light wavelength is often referred to as dispersion slope. Various dispersion management techniques have been used to reduce dispersion and to manage dispersion slope by reducing dispersion at individual channel wavelengths. Dispersion management is particularly important in wavelength division multiplexed (WDM) optical communication systems transmitting multiple channels at multiple wavelengths.
One dispersion management technique involves dispersion mapping where optical fiber types are selected and arranged to manage the dispersion as a function of distance in the transmission segments of an optical communication system. One example of a transmission segment design mixes spans of non-zero dispersion-shifted fiber (NZDSF) with spans of dispersion compensation fiber (DCF) to realize periodic dispersion compensation over the length of the optical transmission segment. The length of each period in such periodic dispersion maps may be in the range of about 500-1000 km per period.
The use of such periodic dispersion maps to manage dispersion in branched optical networks presents problems. A branched optical network may include a plurality of network nodes such as terminals and/or branching units and transmission segments coupled to the network nodes. One complication in the design of a branched optical network using the standard periodic dispersion map is the difficulty in satisfying the requirements for periodic dispersion compensation. Another problem is the limit on accumulated dispersion along all fiber paths for every digital line section (i.e., full fiber path) through the branched network. Changing a branching unit location in a periodic dispersion map design, for example, can result in serious changes to the transmission line design and/or production plan in order to comply with periodicity requirements. Alternatively, the periodicity requirements may be compromised to allow implementation of changes necessary to meet cost and schedule considerations. The periodicity requirements and accumulated dispersion also present problems when networks implement fiber switching or dynamic reconfiguration of channel routing at the branching units.
Accordingly, there is a need for dispersion management in a branched optical network that facilitates changing or reconfiguring the branched network.